Thioglycosyl donors

Finally, a novel sequential glycosylation procedure has been reported using 1-hydroxyl and thioglycosyl donors [230], Yamago et al. reported a broad substrate scope utilizing the BSP/Tf20 promoter system to preactivate thioglycosyl donors... 

In this case, the 6-O-trityl group improved the a-sclcctivity of the glycosylation because of the steric effects. The trityl ether of the resulting product can act as an acceptor when it is glycosylated with a fully benzylated thioglycosyl donor using NIS... 

Scheme4.25 The preparation ofthe Galili pentasaccharide using thioglycosyl donors and acceptors in a two-directional glycosyl-ation strategy.

R. Roy, F. O. Andersson and M. Leteilier, Active and latent thioglycosyl donors in oligosaccharide synthesis. Application to the synthesis of a-sialosides. Tetrahedron Lett. 33 6053 (1992). 

The allyl glycoside of a-D-Abe-(l ->3)-a-D-Man 115 was prepared by a different approach.200 The ethyl 1-thio-D-abequopyranoside donor 113 was obtained from methyl (3-D-galactopyranoside derivative 110 according to Scheme 33. The cyclic sulfate intermediate 111 was the precursor for the stereoselective reduction with tetrabutylammonium borohydride to 112 which was further derivatized to the thioglycosyl donor 113. Donor 113 was reacted with acceptor 114 to give 115 after deprotection. 

Perhaps more troublesome than the moderate yields is the necessity for reversed-phase high-performance liquid chromatography (HPLC) to purify the Fmoc protected amino acid glycosides. It has been reported,23 that the carboxylic acid moiety of an amino acid can be protected as a phenacyl ester and after glycosylation be removed with HOAc/Zn° (Scheme 5.7). Thus, a thioglycosyl donor, having a nonparticipating functionality at C(2), was reacted with the Fmoc protected phenacyl ester... 

Cao, S, Hemandez-Mateo, F, Roy, R, Scope and applications of active and latent thioglycosyl donors, part 4. J. Carbohydr. Chem., 17, 609-632, 1998. 

Z. Wang, L. Zhou, K. Ei-Boubbou, X. S. Ye, and X. Huang, Multi-component one-pot synthesis of the tumor-associated carbohydrate antigen Globo-H based on preactivation of thioglycosyl donors,... 

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